This application relates to the art of power regulation and, more particularly, to the regulation of the output voltage from alternators. The invention is particularly applicable to voltage regulators for use in conjunction with alternators and will be described with particular reference thereto. It will be appreciated, however, that the invention has broader applications and may be used in conjunction with other power generating apparatus and in other power regulation applications.
Alternators commonly have three stator windings which are connected to a Y or delta configuration. A voltage is induced in the stator winding by rotation of the magnetic field generated in a rotor. The rotor has a small amount of residual magnetism which is sufficient to generate a small voltage in the stator windings. Further, field windings are provided to increase the magnetic field when a field current flows through the field windings. The increased magnetic field increases the voltage output from the stator windings. Other alternator designs have used a power transistor to control the flow of the field current to the field windings. A shunt transistor has been used to switch the power transistor between its conductive and nonconductive states as the output voltage of the stator windings rises above or falls below a predetermined output voltage.
One of the principal problems with prior art voltage regulators has been in the relatively high failure rate of the power transistors. More specifically in this regard, it has been found that when the power transistor was supposed to be in its fully conductive state, the shunt transistor was actually still conducting some current. Such conduction removed some of the base current from the power transistor to cause an increased voltage drop thereacross. This voltage drop, in turn, caused the power transistor to generate additional heat and eventually to fail.
The present invention contemplates a new and improved alternator voltage regulator which overcomes the above referenced problems as well as others and provides such a regulator which is reliable, long-lived, simple to build, and economical.